Variable displacement pumps

ABSTRACT

THIS INVENTION PROVIDES A VARIABLE-DISPLACEMENT-PUMP THROUGH WHICH LIQUID IS INTENDED TO FLOW IN ONE DIRECTION ONLY, A CHANGEOVER VALVE ADAPTED TO JOIN THE PUMP DELIVERY TO EITHER ONE OF TWO PASSAGES AND A CONTROLLING MEMBER CONNECTED TO THE CHANGEOVER VALVE AND ALSO CONNECTED TO ADJUST THE DISPLACEMENT OF THE PUMP. THE ARRANGEMENT IS SUCH THAT MOVEMENT OF THE CONTROLLING MEMBER IN ONE DIRECTION FROM A NEUTRAL POSITION CAUSES THE PUMP DELIVERY CONNECTION TO BE JOINED TO ONE PASSAGE AND IN THE OTHER DIRECTION FROM THE NEUTRAL POSITION CAUSES THE PUMP DELIVERY CONNECTION TO BE JOINED TO THE OTHER PASSAGE, AND MOVEMENT OF THE CONTROLLING MEMBER IN EITHER DIRECTION FROM THE NEUTRAL POSITION CAUSES THE PUMP-DISPLACEMENT TO BE INCREASED.

United States Patent [72] Inventor John Christopher Eglington Flint Chalford Hill, Stroud, England [21] Appl. No. 808,781 [22] Filed I Mar. 20, 1969 [45] Patented June 28, 1971 [73] Assignee Dowty Technical Developments Limited Brockhampton, Cheltenham, England [32] Priority Mar. 27, 1968 [33] Great Britain 1 1 [4,626/68 {54] VARIABLE DISPLACEMENT PUMPS 9 Claims, 4 Drawing Figs.

[52] 11.8. CI 137/565 [51] Int. Cl E031) 5/00, E03b 11/16, F04b1/30 150] Field ofSearch l03/38.2, 162;60/52;417/269, 270; 137/565 [56] References Cited UNITED STATES PATENTS 2,316,926 4/1943 Willett 60/52 Primary Examiner--William L. Freeh AttorneyYoung and Thompson ABSTRACT: This invention provides a variable-displacement-pump through which liquid is intended to flow in one direction only, a changeover valve adapted to join the pump delivery to either one of two passages and a controlling member connected to the changeover valve and also connected to adjust the displacement of the pump. The arrangement is such that movement of the controlling member in one direction from a neutral position causes the pump delivery connection to be joined to one passage and in the other direction from the neutral position causes the pump delivery connection to be joined to the other passage, and movement of the controlling member in either direction from the neutral position causes the pump-displacement to be increased.

PATENTED JUN28 l97l SHEET 2 OF 3 INVENTOR JOHN Cuusromse Ecuuarou Fum- ATTORNEYS PATENTEU JUNZBISYI 3.587.636

swan 3 OF 3 INVE NTOR JOHN Cums-ram Eaunarou FLINT %I'W7, I

ATTORNEY}? VARIABLE DISPLACEMENT PUMPS This invention relates to a variable-displacement pump. The object of the invention is to provide a simple pump through which the liquid is intended to flow in one direction only and adapted to deliver liquid at variable flow rate and pressure to either of two passages which may be connected for example to operate a hydraulic motor either in the forward or the reverse direction.

In accordance with the present invention there is provided a variable-displacement pump through which the liquid is intended to flow in one direction only, a changeover valve adapted to join the pump delivery connection to either one of two passages and a controlling member connected to the changeover valve and also connected to a pumpisplacement control device, movement of the controlling member in one direction from a neutral position causing the pump delivery connection to joined to one passage and in the other direction from the neutral position causing the pump delivery connection to be joined to the other passage, and movement in either direction away from the neutral position causing the pumpdisplacement control device to be moved in a pump-displacement-increasing direction.

The pump-displacement control device may comprise a servo control member arranged to control a servomotor which is in turn arranged to adjust the displacement of the pump.

Movement of the pump approaching the minimum displacement position as a result of movement of the control member to the neutral position, may open a pump unloading passage. The unloading passage may include a variable restrictor adjusted by movement of the control member to cause movement of the servomotor. The unloading passage may include a further restrictor connected in between the pump delivery and the variable restrictor and the restrictive elfect of which is reduced as the minimum displacement position is approached.

The controlling member may be connected to the pump-displacement control by the wire of a Bowden cable, the controlling member being arranged to pull the end of the wire adjacent to the controlling member away from the sleeve whenit moves in the one direction and being arranged to push the corresponding end of the sleeve over the wire away from said end when it moves in the other direction, the other end of the sleeve being fixed.

An embodiment of the invention will now be particularly described with reference to the accompanying drawings in which,

FIG. 1 is a diagrammatic view showing a part of the pump in elevation and the servomotor in cross section,

FIG. 2 is a cross section through the reversing valve,

FIG. 3 is an end elevation of the reversing valve, and

FIG. 4 is a circuit diagram of the pump, servomotor and valve shown in FIGS 1, 2 and 3.

Reference is made initially to FIG. 1 of the accompanying drawings. The pump illustrated at l is constructed substantially in accordance with the drawings of the complete specification filed in pursuance of our application 694,7l7. This pump includes a valve block 2, a casing 3 and lugs 4 formed on the casing to carry a swash plate 5. Valve block 2, casing 3 and lugs 4 are integrally formed. A lever 6 extends from the swash plate 5. Secured to the valve block 2 is a servomotor 7. The servomotor casing comprises a fixed cylinder 8 within which a hollow piston 9 is slidably mounted. The cylindrical connection rod 11 formed integrally with the piston extends through a sealed opening 12 in the end of the cylinder 8 near to the lever 6. The end of the connecting rod 11 is pivotally connected to pin 13 to a link 14 which in turn is pivotally connected by a pin 15 to the end of the lever 6. Within the cylinder 8 a working space is defined between the piston 9, the cylinder 8, the connecting rod 11 and the sealed opening 12 in the end of the cylinder. Liquid at pressure from the delivery connection from the pump 1 is fed to the connection 17 of the cylinder 8 and liquid may flow to the working space 16 from the connection 17 through a fixed orifice 18.

The controlled member is a hollow cylindrical slide valve 22 mounted within a cylindrical bore 23 in the piston rod 11 adjacent to the piston 9. A transverse bore 24 in the connecting rod 11 connects the bore 23 to the working space 16. Piston valve 22 also includes a transverse bore 25 which communicates with a central bore 26. The bore 26 opens through a drilling 27 into the interior of the hollow piston from which access is obtained through the open end 28 of the cylinder to reservoir. The piston valve 22 is mechanically connected to the piston 9 by means of a cross pin 29 which is a tight fit within the piston valve but is capable of longitudinal movement within elongated holes 31 in the piston. A flexible wire 32 is secured to the pin 29 and extends through the open end 28 of the cylinder 8.

In the midposition of the pin 29 with the lost motion permitted in the holes 31 there is. a small overlap as shown in between the ports 24 and 25 which produces a first restrictor whose restrictive effect is about the same as the orifice 18. In order to-increase the displacement of the pump the wire 32 is pulled to the left as seen in the drawing to move the pin 29 to the end of its lost motion in the holes 31. This movement will reduce the overlap between ports 24 and 25 thus increasing the restrictive effect and the pressure in the working space 16 thereby increases towards the value of pressure supplied at connection 17. The pressure reacting on the annular area of piston 9 exposed to working space 16 will cause piston 9 and connecting rod 11 to move to the left as seen in the drawing to increase the tilt of the swash plate 5. If tension is relaxed on the wire 32 a slight further movement of the piston 9 will take it to the position where the pin 29 is midway within the lost motion given by holes 31 and the ports 24 and 25 will increase their overlap thus reducing the restrictive effect of the first restrictor and reducing the pressure in the working space 16. Since the pump is a swash plate pump and since the pivot of the swash plate is deliberately offset it is arranged that there is a considerable restoring force tending to move the'swash plate towards its minimum displacement position. Thus at the selected value for pump-displacement the overlap between the ports 24 and 25 will be self-adjusting by slight movement of the piston 9 to adjust pressure in the working space 16 so that the force on the connecting rod 11 is exactly equal and opposite to the force exerted by lever 6 at pin 15. In order to reduce selected displacement the flexible wire 32 is pushed into the open end of the cylinder so that spring 63 may move the piston valve 22 to give a greater overlap between ports 24 and 25. It will be appreciated that the piston valve 22 is hydraulically balanced and it needs very little force to urge it into the bore 23. The greater overlap of the ports 24 and 25 effectively reduces the restrictive effect of the first restrictor thereby reducing pressure in the working space 16 and enabling the self-restoring force of the swash plate 5 to reduce the selected displacement for the pump.

Reference is now made to FIGS. 2 and 3 of the accompanying drawings. The valve body 33 is formed with a valve bore 34 whose two ends are connected to a reservoir connection 36. A pair of service ports 37 and 38 open into the bore 34 and are connected respectively to passages 39 and 41. Centrally the bore opens into an actuating chamber 42. A pump delivery connection 43 opens into the actuating chamber 42, a ball check valve 44 serving to prevent reverse flow from chamber 42 into connection 43. A piston valve 45 is slidably mounted in the bore 34, the valve having a pair of spaced lands 46 and 47 for cooperation with the ports 37 and 38. The lands are connected together by a rod 49 having a central slot 51 to accommodate the ball end 52 of an actuating lever 53. The lever 53 is carried by a shaft 54 which extends through a suitably sealed opening in the wall of the chamber 42.

Externally of the valve body 33 the shaft 54 carries the control member in the form of a lever 55. Loosely mounted on the shaft 54 are a pair of movable supports in the form of levers 56 and 57 which at their remote ends carry respectively cable connectors 58 and 59. The connector 59 is connected to the flexible cable 32 which at its opposite end engages the pin 29 of FIG. 1. The cable connector 58 engages the end of the flexible sleeve 61 through which wire 32 passes to form a Bowden cable. The end of the sleeve 61 opposite to the connector 58 is fixedly secured at a convenient support 60 (FIG. 1) adjacent to the end 28 of the cylinder 8. A cylindrical abutment 62 integrally formed with the valve casing 33 extends between the levers 56 and 57. A compression spring 63 is fitted around the wire 32 at the end thereof entering the cylinder 8, this spring exerting a force between the wire 32 and the sleeve 61 tending to pull the wire 32 from the sleeve 61. This results in a tension force in wire 32 and a compression force in the sleeve 61 which forces react on the supports 58 and 59 to urge them together so as to cause or tend to cause both levers 56 and 57 to engage the abutment 62. The lever 55 carries a cylindrical abutment pin 64 which extends between the levers 56 and 57 and which can engage either of these two levers depending on the direction of movement of lever 55.

FIG. 4 is a circuit diagram of a complete transmission incorporating the motion converting mechanism, the pump, servomotor and the control valve illustrated in FIGS. 1, 2 and 3 and arranged to feed reversible actuator or hydraulic motor 81 from the two passages 39 and 41. A pair of oppositely directed relief valves 82 and 83 are connected across the passages 39 and 41 within the valve body 33 to serve to prevent the pressure exceeding a predetermined high value in either direction across the hydraulic motor 81.

In FIGS. 1 and 2 the servomotor is shown in the position corresponding to. minimum pump-displacement and the reversing valve and its operating lever are shown in the position corresponding to neutral. In this condition the two lands 46 and 47 completely close the ports 37 and 38.

Assume now that forward movement of the hydraulic motor is required. The lever 55 is moved upwardly as shown in FIG. 2 and the initial part of the movement until the abutment 64 makes contact with the lever 56 will move the piston valve member 45 so that port 37 is connected to the chamber 42 and port 38 is connected to the passage 36. Further movement oflever 55 will then operate on the lever 56 moving the sleeve 61 whilst the wire 32 at the connector 59 remains stationary. The Bowden cable between the connector 58 and the anchorage at the sleeve adjacent to the servomotor 7 is arranged to have a slight loop. In this way movement of the end of the sleeve 61 at connector 58 is converted into movement of the wire 32 at its end thereof connected to the pin 29 in the servomotoL-This movement will be applied to the servo valve 26 to reduce the overlap of ports 24 and 25 thus reducing the leakage flow from the pump delivery. Pressure will then rise in the working space 16 and the piston 9 will move to the left as seen in FIG. 1 to raise the displacement of the pump 1 from its minimum value. The liquid at pressure delivered by the pump 1 then passes through connection 43 and check valve 44 into the chamber 42 and from chamber 42 into the service port 39 where it will cause operation of the motor 81. Return flow from the motor 81 entering the passage 41 will then flow through passage 36, to the reservoir. Further movement of the lever 55 will then determine the displacement required for the pump 1.

If reverse movement of the motor 81 is desired the lever 55 is moved downwardly from the FIG. 2 position, initial movement acting on the piston valve 45 so that port 38 is connected to chamber 42. Immediately the abutment 64 engages lever 57 tension will be applied to the wire 32 which will apply tension to move the servo valve 26 in the same direction as described for forward movement to cause the pump-displacement to increase from its minimum value. The liquid delivered at pressure from the pump 1 through check valve 44 and chamber 42 will pass through passage 41 to the motor 81 to drive it in the reverse direction. Return flow from the motor entering into passage 39 will pass through passages 35 and 36 to the reservoir.

I claim:

1. A nonreversible variable displacement pump through which liquid is intended to flow in one direction only, a changeover valve adapted to oin the pump delivery connection to either one of two passages, a displacement-adjusting servomotor for the pump, a variable restrictor adjustable to cause movement of the servomotor, a controlling member connected to the changeover valve and to the variable restrictor, movement of the controlling member in one direction from a neutral position causing the pump delivery connection to be joined to one passage and in the other direction causing the pump delivery connection to be joined to the other passage, and movement in either direction away from the neutral position causing the variable restrictor to be moved to cause the servomotor to adjust pump displacement in a displacement increasing direction, and a pump-unloading passage opened by movement of the servomotor to the neutral position to unload the pump through the variable restrictor.

' 2. A variable-displacement-pump according to claim 1 wherein the controlling member is connected to the pump-displacement control device by the wire of a Bowden cable comprising a wire slidable in a sleeve, the controlling member being arranged to pull the end of the wire adjacent to the controlling member away from the sleeve when it moves in the one direction and being arranged to push the corresponding end of the sleeve over the wire away from said end when it moves in the other direction, the other end of the sleeve being fixed.

3. A variable-displacement-pump according to claim 2 wherein the said corresponding end of the sleeve is attached to a first movable support engageable by the controlling member when moving in one direction and the said end of the wire is attached to a second movable support engageable by the controlling member when moving in the other direction and fixed abutment means for engagement by the supports when the controlling member is in its neutral position.

4. A variable-displacement-pump according to claim 3 wherein when the supports rest against the fixed abutment means, the controlling member canv move by a predetermined distance from its neutral position before engaging either of the supports.

5. A variable-displacement-pump according to claim 3 wherein the controlling member comprises a pivotallymounted lever and the two movable supports also comprise pivotally-mounted levers.

6. A variable-displacement-pump according to claim 5 wherein the three levers are pivotally-mounted about the same axis.

7. A variable-displacement-pump according to claim 2 including spring means acting between the wire and the sleeve to tend to maintain the two movable supports each in engagement with the fixed abutment.

8. A variable-displacement-pump according to claim 7 wherein the spring means is located adjacent to the pump-displacement control device and comprises a compression spring mounted on the wire to maintain tension in the wire and compression in the sleeve.

9. A variable-displacement-pump as claimed in claim 1, including a further restrictor connected between pump delivery and the variable restrictor, the restrictive effect of which is reduced as the minimum displacement position is approached, said further restrictor and said variable restrictor in series forming said pump-unloading passage. 

